In the generally used conventional method of discharging detrimental gases and dusts, an exhaust hood is provided near the source to suck the gas away. Therefore, there is no directivity at all in the suction so that if separated from the suction apparatus the wind velocity will attenuate so quickly that it is difficult to obtain the required controlled wind velocity. Such large volumes of not only the generated detrimental gases and dusts, but also of ambient air is sucked in so that as a result a large blower and duct are required increasing the many problems inherently found in the equipment and cost attendent thereto.
There has recently been developed a method wherein an artificial tornado is generated in order to exhaust detrimental gases and dusts. For example, a spiral flow is made in the center of a horizontally elongated exhaust hood so as to suck air from the hood. This current can generate, in the enclosed exhaust hood, a sucked wind velocity along its horizontal length, but it has no sucking action in the free space. In this sense, this method is not different from the conventional side hood exhaust system. There is also a device wherein air is blown out in the form of a tornado created by burning the air with a burner or rotating a blowing nozzle. However, these blowing tornado mechanisms, are not in fact tornados in form, and are quite different particularly in their ultimate use.